Hereinafter, compounds represented by Formula (I), Formula (II), Formula (III), and Formula (IV) are referred to as Compound (I), Compound (II), Compound (III), and Compound (IV), respectively. The same applies to the compounds of other formula numbers.
It is known that Compound (II) has protein kinase C-inhibiting activity, and the process for producing Compound (II) as shown above is disclosed in Japanese Published Unexamined Patent Application No. 155284/87. According to the process, Compound (II) is directly produced from Compound (I). However, in the process, Compound (III) wherein a nitrogen atom in the amide group is lower-alkylated, and Compound (IV) wherein both of a hydroxyl group and a nitrogen atom in the amide group are lower-alkylated are produced in large quantities as by-products at the same time. Thus, the yield of the desired Compound (II) is low, and a complicated technique unsuitable for mass production, such as silica gel chromatography, is required for purification.